My point was more about the assumption about who owns somesite.com. Assuming two domains are owned by the same company is a somewhat secondary concern to authen

My point was more about the assumption about who owns somesite.com. Assuming two domains are owned by the same company is a somewhat secondary concern to authenticating the owner of either; both of which are larger issues in their own right. As commented by someone else, see e.g. whitehouse.com. The fact of whitehouse.gov being a different owner is much less of concern than that of whitehouse.com not having the expected owner in the first place (from the perspective of most visitors).